B. microti is a tick-borne parasite that resides in the red blood cells of infected individuals causing a malarial-like sickness called babesiosis (Homer et al., Clin. Microbiol. Rev. 13(3):451-469 (2000)). B. microti is a potential risk to the blood supply as it can be transmitted to humans by the bite of infected ticks, but can also be transmitted by transfusion from infected blood donors to recipients of blood or blood products (Setty et al., Am. J. Clin. Pathol. 120:554-559 (2003)). Infection with B. microti represents one of the most common parasitic infections worldwide among wild and domestic animals, and humans (Homer et al., supra). The number of reported cases of B. microti infection in United States is increasing rapidly, particularly in the Northeast coastal states and the upper Midwest (Krause et al., Am. J. Trop. Med. Hyg. 68(4):431-436 (2003); Herwaldt et al., Am. J. Trop. Med. Hyg. 53(2):146-51 (1995)). Seroprevalence estimates of B. microti among blood donors range from 0.3% in Wisconsin donors to 4.3% in Shelter Island, N.Y. (Cable et al., Current Opinion in Hematology 10(6):405-411 (2003)).
Infection with B. microti often includes co-infection with lyme disease (Krause et al., Clinical Infectious Diseases 34:1184-1191 (2002)) and often remains undetected for extended periods of time. Babesiosis is potentially fatal, particularly in the elderly and in patients with suppressed immune systems (Kjemtrup et al., Int. J. Parasitol 30:1323-1337 (2000)). Patients infected with babesiosis and/or lyme disease share the same symptoms of muscle aches, fever, headaches, and fatigue (Homer et al.,), thus making diagnosis difficult. Anti-malarial drugs such as quinine and clindamycin are most effective in treatment of babesiosis (Med. Lett. Drugs Ther. 34(865):17-26 (1992)). Accordingly, accurate and early diagnosis of B. microti infection is critical.
Microscopy, PCR, indirect immunofluorescence assay, nucleic acid testing and ELISA-based tests are often used in diagnosing B. microti infection (Loa et al., Current Microbiology 49:385-389 (2004)). Microscopic and PCR analysis of blood samples may provide false-negative results when patients are first seen in the clinic. High throughput testing of serum samples from humans for B. microti are not suitable for nucleic acid testing. Because many of B. microti's immunogenic epitopes are cross-reactive with other antibodies such as malaria (Houghton et al., Transfusion 42(11):1488-96 (2002)), ELISAs to detect antibodies of B. microti may not be effective due to unacceptable sensitivity and specificity, especially when antibodies to B. microti are at low titers. Accordingly, there remains a tremendous need to develop compositions in order to detect antibodies against B. microti. 